The invention relates to a process for the production of a mixture to be utilised, for instance, in the production of building materials and comprising at least two burned and/or sintered and/or calcined and/or heated inorganic components of different composition, the first of said components being subjected to a heating process, in particular a burning process, and the second or other component(s) being heated to a temperature below the heating temperature of the first component, and a device for carrying out the process according to the invention.
In many branches of industry, -- no claim to completeness is made in mentioning the refractory, ceramics and building materials industries 13 products composed of two or more materials of different composition are produced. In most cases, these products or their components are formed of the most diverse starting materials by means of heating and/or calcining and/or fritting and/or sintering and/or melting processes, general mention being made here of the production of cement clinkers. These heating processes generally require large amounts of caloric energy -- in the light of rising energy costs, the application of energy-saving measures in carrying out the processes in the preceding branches of industry is a matter of urgent concern.
Just to give an example, it is known that the burning of Portland cement clinker requires temperatures which generally range in an order of magnitude of 1400.degree. to 1450.degree. C. The large amount of heat present in the clinker due to its burning process must be removed from the clinker after leaving the burning zone of the burning kiln, which is generally a rotary kiln, in suitable cooling means such as grate-, rotary-, shaft- or planetary coolers. The heat taken from the clinker is utilised, a.o., for heating the combustion air supplied to the burner. There is often no possibility of utilising or applying the remainder of the heat.
The present invention represents an essential contribution to the solution of the problem of reducing energy requirements, particularly in the branches of industry mentioned above, for the event that one or more of the components of a two- or multi-component mixture (for instance of a binder mixture) is (are) obtained from a starting material for the first component which is heated to relatively high temperatures, while the starting material(s) for the other component(s) is (are) heated to temperatures which are lower in comparison to the heating temperatures of the first component.
The process according to the invention of the type initially mentioned comprises the improvement that under utilisation of the heat applied in the heating process, (for instance, in a burning process), of the first component to be heated to higher temperatures or of the heat liberated in the cooling of the first component, the starting materials for the other component(s) which is (are) to be heated to lower temperatures as compared to the first component, are added to or admixed with the first component which has already been heated and preferably is leaving the heating-, in particular the sintering or burning zone of a heating means, thus establishing an intimate contact within the area of the cooling zone of the process, that is the zone extending before, during and/after entry of the first hot component into a cooling means downstream of the heating means. But in the event that more than one other component is to be added, these components can be added in two or all three of the zones indicated above.
Components are understood to mean materials of the most diverse nature, i.e. chemical substances, mixtures of substances, physical blends, multi-phase systems and/or other heterogeneous materials.
The "cooling zone of the process" is understood to mean the following: it starts there in the heating zone (burning kiln) where the first component has passed the maximum temperature on its way through the kiln and extends over the transition zone between burning kiln and cooling means and into the cooling means up to the end of the cooling means or cooling process, respectively.
In addition to the advantages mentioned, the combination of the product streams of first heated component and added further components during production brings with it a considerable streamlining and improved economy over the separate production processes used for the production of the individual components up to now.
It is possible to charge the entire amount or only part of the starting materials for the other component(s) to be heated to lower temperatures into the cooling zone of the process provided according to the invention. A remaining part can be added to the first component even prior to its being subjected to the heating process and can be treated at higher temperatures or, after having been subjected to a separate heating process, can subsequently be added to the mixture according to the invention of at least two components. As already mentioned, parts of the starting materials to be heated can be added in several of the zones indicated above.
Application of the process according to the invention is particularly advantageous where the starting materials for the first and/or the other component(s) are formed of materials which are to be subjected to an intended conversion process by means of heating.
By the addition of the starting materials for the other component(s) which are to be heated to lower temperatures as compared to the first component -- to be called "starting materials" for short in the following -- to the hot first component as provided for according to the process of the invention, an intimate contact of the materials and thus a very effective transition of the heat energy stored in the first component from the first burning process to the starting materials which are generally charged in a cold state into the area of the end of the heating process, for instance of a burning kiln, is achieved. As a result and as intended, the freshly heated first component, for instance a freshly burned Portland cement clinker of conventional composition, is cooled off before, during or after its entry into or transition to the cooling means, (which in the case of Portland cement clinker is a clinker cooler), as a result of its contact with the cold starting materials, while the starting materials for the other component(s) are heated to the intended temperatures. In many cases, such as when producing Portland cement clinker or burning lime, a rapid cooling off of the first component is desirable and can easily be effected according to the invention. Due to the intimate heat exchange with the starting materials for the other component(s), wear on the cooling zone as defined above, regardless of whether it is located in the discharge part of the kiln or formed by a cooling means, is essentially reduced and the efficiency of the cooling zone is materially raised. Just to give an example, the kiln exit temperatures of Portland cement clinker of conventional composition are about 1300.degree. C. Moreover, due to the intensive transfer of heat energy from the hot first component to the starting materials for the other component(s) by selection of the site of addition, heating of the latter component(s) or parts thereof in a separate process or processes can be totally omitted.
The process according to the invention, which combines two different heating operations into one single process, makes possible a substantial reduction of energy requirements, technical equipment, operating personnel and thus, of expenditure.
In the following, particularly preferred embodiments of the process according to the invention are described. In cement production, it is of advantage to produce a building material mixture comprising at least two components of different composition, one of which is a Portland cement clinker of conventional composition, while the other component(s) is (are) to be heated to a temperature below the burning temperature of the Portland cement clinker. The production process comprises the improvement that the starting material(s) intended for the component(s) to be heated to lower temperatures as compared to the burning temperature of the Portland cement clinker is (are) added to or admixed with the hot Portland cement clinker of conventional composition leaving the burning or sintering zone of the burning kiln before, during or after its entry or transition into a cooling means formed by a clinker cooler. The freshly burned hot Portland cement clinker of conventional composition serves as the primary hot substance from which heat energy is transferred to the starting material(s) for the other component(s) and there effects the intended conversion processes.
Suitable starting material(s) for the component(s) which is (are) to be heated to lower temperatures as compared to the heating temperature of the first component, according to the invention and a particularly preferred embodiment of the process of the invention, is (are) material(s) which become(s) hydratisable as a result of the heating process. These materials are marl clinker raw materials selected from the group comprising marls, lime marls, dolomitic marls, argilliferous marls, marl slates, shales, calciferous clays, argilliferous limes, phyllites, lime phyllites, ultramafic rocks and waste products which are similar in their composition to the materials enumerated.
The chemical composition (empirical formula) of the marl clinker raw materials enumerated above can vary within a wide range. Marl clinker raw material, just like conventional Portland cement raw meal, mainly consists of compounds of silicic acid, alumina, ferric oxide and lime, but is of lower calcium content than conventional Portland cement raw meal.
"Hydratisable" is understood to mean that the products or compounds formed in the marl clinkers as a result of the heating by the first hot component are capable of reacting with water to form compounds resistant to attack by water, the hydraulicity optionally being stimulated or enhanced in a manner known per se by means of alkaline and/or sulfatic substances. The hydratisable substances differ by this inherent hydraulicity from substances such as, for instance, certain silicic acid modifications (opal) or kaolin, whose structure is merely opened by means of heating and which are thus capable of reacting with calcium hydrate only. In characterising the new formations formed in the marl clinkers, it should be noted that they contain compounds which contain substantially less CaO as compared to Portland cement clinkers of conventional composition, particularly ternary compounds of low calcium content on the basis of SiO.sub.2, Al.sub.2 O.sub.3, CaO, (Fe.sub.2 O.sub.3), calcium silicates of low calcium content and calcium aluminates of low calcium content. If, for instance, Portland cement clinker of conventional composition is used as the first component, mixed clinkers are obtained which when processed into cements often even surpass the Portland cement clinker in their final properties, such as strengths.
Due to the burning temperature of the marl clinker which is low in comparison to the burning temperature of the Portland cement clinker of conventional composition, it is possible to use dolomitic marls with MgO contents substantially higher than those admissible up to now in Portland cement clinker production without detrimental effects due to magnesia expansion on the concrete produced from this cement.
According to a further embodiment of the process according to the invention, it is possible to use as the first component heated to higher temperatures conventional limes, marl limes or dolomitic limes which are subjected to a burning process and converted to white (fat)limes, water limes or (highly) hydraulic limes at temperatures within a range of about 1100.degree. to 1200.degree. C.
Preferred as suitable starting materials for the other component(s) to be heated to lower temperatures to be added to the hot burned limes are the marl clinker raw materials mentioned above. They are heated to the desired temperatures by contact with the decarbonated lime leaving the burning zone.
The product or mixture of at least two components of different composition thus obtained is suitable for the production of plaster and masonry binders, but also of mixed binders of high quality and, due to the particular qualities of the marl clinker share, is of high suppleness and good workability. Good workability and high yield can be further increased by additions known per se such as air entraining agents, cellulose derivatives or similar additions.
To the hot first component mentioned above, e.g. hot Portland cement clinker of conventional composition, not only marl clinker raw materials but also the starting materials for the other component(s) described in detail in the following of the mixture according to the invention for the production of building materials can be added in the respective(cooling)zone of the process in the same way as addition to the hot Portland cement clinkers of conventional composition or burned lime is effected. To the mixture thus obtained, further components can be added in order to obtain commercial building materials. The lasting advantage in this is the energy saving made possible by the combined heating-cooling process according to the invention.
It should be mentioned here that it is of course possible within the wide framework of the invention to use as the first component(s) to be heated to higher temperatures those substances which have been described or still are to be described in the following as the "second" or "other" components added to the first components. In this case, for instance, marl clinkers burned from the marl clinker raw materials previously mentioned as the starting materials for the other component(s) can be used as the first (hotter) component for heating starting materials for substances to be heated to lower temperatures to the respective desired temperature. For example, the marl clinker hot from the burning process can be used to expand perlite or slate as the other component.
According to a further preferred variant of the process according to the invention, materials to which pozzuolana properties are imparted by the heating process can be used as the starting materials for the other component(s) (to be heated to lower temperatures). These particularly include materials of silicate and/or aluminate quality selected from the group comprising silicic acid modifications, felspars, argilliferous materials which can be used for the production of bricks, oil shale residues, bauxites, laterites, trasses, volcanic extrusive rocks, glasses and substances which already possess pozzuolana qualities. It was found that the pozzuolana properties of most natural and artificial pozzuolanas can be essentially enhanced by the new type of heat treatment according to the invention.
A further embodiment of the process according to the invention provides starting materials for the other component(s) which expand during the heating process and thus decrease their apparent density so that they can serve in the product comprising at least two components of different composition as, for instance, concrete lightweight aggregates, bulk material or for heat insulation purposes. Such starting materials particularly are clay with a propensity to expansion, (expansible clay,) expansible slate (shale), expansible perlite, expansible tuff, expansible vermiculite or other expansible materials.
Finally, it becomes possible according to the process of the invention to use as starting materials substances which have a detrimental effect on quality, but lose this deteriorating effect as a result of the heating process and thus make possible their utilisation in connection with Portland cement clinker of conventional composition. Such materials which might be detrimental to quality but lose their deteriorating effect during the burning process are materials susceptible to combustion, to conversion to the gaseous state, to conversion to vapour, to chemical reaction or to any other change in the course of the heating process. Examples for such compounds are fly ashes with a high content of sulfur compounds or combustible components which cannot be used as cement grinding additions at the present time due to these deteriorating properties.
In the process according to the invention, the starting materials can be added to the first component, which, as already mentioned, can be a Portland cement clinker of conventional composition, in a coarse state, in particles of about 5 to 30 mm, preferably 10 to 20 mm grain size. In this case, the surface of the starting materials is generally heated quicker and to higher temperatures than the inside of the particles. When the proper temperature range is adjusted by selection of the place of addition within the cooling zone of the process, the surface of the particles will be denser and more abrasion-resistant after heating than the inside of the particles. This can mean an essential reduction of possible undesirable comminution or formation of dust due to abrasion.
According to a preferred variant of the process of the invention, the starting material(s) for the other components, particularly in the case of the addition of marl clinker raw materials, are added to the first hot component, which can be a Portland cement clinker of conventional composition, fast and/or at comparatively high temperatures, whereby due to the rapid cooling off of the first component, which is particularly important in the case of Portland cement clinker of conventional composition, this component is improved in its quality and the other component(s), particularly in the case of marl clinker raw materials, due to the fast heating is (are) provided with an outer layer which is higher burned and more abrasion-resistant as compared to the inside of the particles. A fast addition has similar favourable effects, for instance, on the various expansible materials indicated above.
A regulation of the temperature to which the starting materials of the other component(s) are heated by contact with the hot first component can be achieved, on the one hand, by the amount of starting materials added and, on the other hand, by selecting the site of addition within the cooling zone. If, for instance, a low heating temperature of the starting materials is intended, such as in the case of expansible materials, these substances will be added immediately prior to or at the entry of the stream of the first hot component into the cooling zone or immediately into the cooling zone. In this case, a comparatively large amount will be added. If the heating temperature of the starting material(s) of the other components is to be high, a small amount will be added or these starting materials will be added to the first hot component, for example, hot Portland cement clinker, either still within the heating zone, e.g. in the burning zone, or immediately after its leaving the heating zone, e.g. the burning zone. The weight ratio of first and other component(s) can vary within a wide range.
When a mixture of Portland cement clinker and marl clinker is produced, an addition ratio (related to weight) of marl clinker raw materials to Portland cement clinker of conventional composition of 1 : 1 to 1 : 25, particularly of 1 : 2 to 1 : 25, is established. Particularly favourable results, especially in respect to economy at simultaneous achievement of high strengths, can be obtained with weight ratios of 1 : 4 to 1 : 10 (each marl clinker to Portland cement clinker of conventional composition). The cements thus produced are similar to Portland cements, but superior to those in respect to workability and other properties.
The addition of the starting materials into the range of the or after the heating zone, for instance at the discharge end of the kiln or before or at the entry of the first substance into the cooler, can be effected in the most diverse ways, for instance by mechanical or pneumatic conveying such as throwing, propulsion or blowing.
A further object of the invention, for producing the mixture and for carrying out the process explained in detail above, is a device which comprises a heating means, particularly a burning kiln, for instance in the form of a shaft kiln, a rotary tubular kiln or a fluidized bed kiln, for heating the starting materials for the first component, a cooling means and preferably a transition means arranged between the discharge end of the heating means and the adjacent cooling means (formed, for instance, by a clinker cooler). This device according to the invention is so embodied that a feeding means for the addition of the starting materials for the other component(s) is provided.
According to the invention, the discharge end of the feeding means is arranged within the area of the cooling zone of the process.
The discharge end of the feeding means, depending upon the temperature to which the starting materials mentioned above are to be heated, can be arranged within that part of the cooling zone still within the kiln, i.e. within the area of the end of the kiln, within the transition means or within the cooling means. But in some cases, the starting materials can also be added by means of more than one feeding means each arranged in the respective places.
It is of advantage to use a conveyor screw as a feeding means.
Particularly simple of construction and easy to operate is a stationary conveying organ. This can be a chute, a feed pipe (gravity tube) of any given cross section, but also a slide or a gutter.
The feeding means can also have the form of a hood arranged on the shell of the discharge end of a rotary kiln or on the shell of a rotary tubular cooler and of a shovel-shaped fixture penetrating this shell and leading into the interior of the cooler.
If, for example, a chute is used for charging the starting materials for the other component(s) for instance into the area of the discharge end of the kiln, an intimate mixing of the hot first component and said starting materials is effected still within the discharge end of the kiln due to rotation of the kiln when a rotary tubular kiln is used.
Preferred is a device according to one of the embodiments described above, said device having feeding means for the addition of the starting materials for the other component(s) adjacent the transition means arranged between kiln and cooling means under interposition of at least one sealing means.
Sealing means according to the invention, particularly for a gas-tight charging of the raw materials into the desired area of the cooling zone, are preferably double pendulum flap valves or cellular wheel sluices.
When the rotary kiln is provided with planetary coolers, the present invention provides for a preferred embodiment in which the feeding means or the discharge end thereof leads to the area of the feed openings from the rotary kiln to the coolers, so that the addition of the starting raw materials for the first component is effected in the area of the feed openings from kiln to cooler.
A further preferred embodiment of the invention is a device comprising at least one coil or screw wing built into the inside of the shell of the kiln and turning together with the kiln shell, said coil(s) or screw wing(s) conveying the starting materials for the other component(s) -- which are charged at the discharge end of the kiln -- to the feed openings from the rotary kiln to the planetary coolers. If several coils or screw wings are provided, their discharge ends can be arranged in such a manner that they each convey the starting materials to one particularly selected feed opening of the planetary coolers. This is of particular advantage if the share of other component(s) to be heated is relatively small and the raw materials are not to be heated to very high temperatures. Further, in addition to secure conveying of the starting materials for the other component(s), it is preferred that the discharge end of the rotary kiln be conically shaped and that this part of the kiln shell thus be of an inclination compensating for the slant of the kiln, the starting materials for the other component(s) charged at the end of the kiln, for instance marl clinker raw materials, thus being conveyed to the feed openings of the planetary coolers.
In view of the regulation of the amount of starting materials added and thus of the control of the temperature to which the starting materials are heated, it is particularly preferable to use a device which is characterised in that the feeding means for the addition of said starting materials is connected to the kiln or the transition means under interposition of at least one metering means.
The invention is described in detail in the following by means of embodiments of devices according to the invention for carrying out the process according to the invention under reference to the accompanying drawings in which